Value of the physical basis of equivalent uniform dose as applied to intensity modulated radiation therapy

Objective: To study the mathematic and physical basis of the equivalent uniform dose (EUD) and its optimization mechanism in the control of dose distribution in the organs at risk (OAR) and targets in IMRT optimization process, as well as its significance in clinical application. Methods: The mathematic limit analysis method and MATLAB mathematic analysis software were applied to observe the consistence with two different methods. The results of all formulae introduced by Niemierko were compared with the numerical value directly computed. The optimization mechanism of the dose distribution in the target/OAR in IMRT optimization process on the base of 2 units most simplified EUD optimization analysis model was studied. Results: When parameter α tends to + ∞, -∞, 0 and 1, the result of EUD directly computed on the MATLAB mathematic analysis software was similar to that relied on the limit analysis on condition, which provided evidence for experience that we should apply a positive value to OAR and a negative value to targets. By giving a suitable parameter 'α' and 'n', we may get a better target coverage and improve the sparing of critical structures through small number of iterations while using multiple dose-volume constrains for each anatomic structure and with considering great trial-and-error to adjust a larger number of objective function parameters, all of which were helpful to improve the target control probability and reduce the normal tissue complication probability. Conclusions: The use of parameter 'α' does significantly influence the optimization results on EUD based optimization method for patients with head and neck cancer and prostate cancer. Meanwhile, the EUD based optimization method has significant advantages in aspects of optimization results and optimization efficiency when compared with DVH based optimization, which does have greater significance in clinical application. (authors)